Magma's Heat May Help Sustain Sea Life, Study Finds

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Magma that heats seafloor mud could help pump large amounts of
heat-trapping greenhouse gases into the oceans, enriching what
may be a new kind of ecosystem and potentially contributing to
shifts in climate, a new study finds.

Researchers analyzed photographs and seismic and sonar data of
the seafloor of Guaymas basin in the Gulf of California, near
where
the ocean bottom rifts. They unexpectedly saw hot magma
flowing under seafloor mud for up to 30 miles (48 kilometers) on
both sides of the 34-mile-long (55 km) rift. This is 10 times
farther than magma flow seen in ridges without sediment cover,
probably because such mud blankets — some 0.6 to 1.2 miles (1 to
2 km) thick — keep seawater from cooling and solidifying the
molten rock.

The molten rock apparently heated up the seafloor mud, prompting
the organic material-rich sediments to release carbon dioxide and
methane,
greenhouse gases that trap heat from the sun and contribute
to global warming. This methane seemed to help support a
seafloor community of bacteria, tubeworms and other life.

These "may represent a distinct type of ecosystem," said
researcher Daniel Lizarralde, a geophysicist at Woods Hole
Oceanographic Institution in Massachusetts. The newfound
ecosystem is potentially home to species adapted to the unique
thermal and chemical gradients found at such "warm seeps."

The researchers estimate that such heating at this site could
release as much as 88,000 tons (80,000 metric tons) of carbon
annually.

More seep sites

There are probably quite a few more sites like Guaymas around the
world, such as in the South China Sea, the Philippine Sea,
the
Red Sea, the Aegean Sea and the Lau Basin (by the Tonga
Islands in the southwest Pacific).

In total, such rifts probably extend thousands of miles and
release thousands of times more carbon than seen at Guaymas,
Lizarralde said.

"These may represent a whole vast region where you can have this
distinct type of 'warm seep' community that hasn't been explored
yet," Lizarralde told OurAmazingPlanet.

Greenhouse gas release

Hot rock pumped into sedimentary basins has been linked to huge
natural pulses of methane that may have generated dramatic shifts
in global climate in the past, such as at the Karoo basin in
South Africa 183 million years ago and at the Norwegian margin 55
million years ago. Still, the amount of carbon the Guaymas site
pumps out pales in comparison to fossil fuel combustion, which
now surpasses 9 billion tons (8 billion metric tons) of carbon
released per year. It also remains uncertain as to how much of
this carbon might ultimately escape into the atmosphere and how
much the seafloor organisms capture.

Although the carbon from these rifts probably has little direct
impact on
current global warming concerns, "our results may help
understand the past, which is useful for trying to predict the
future," Lizarralde said.

In addition, while rifts can release global warming gases,
scientists have suggested they could also serve as sites where
people could bury such gases and help fight climate change. Some
rifts are linked with a moderate to large amount of magma, and
Lizarralde advised it would be a bad idea to try to dump carbon
in these kinds of systems. However, other rifts are very
magma-poor, and a potentially useful rock from the mantle known
as peridotite is exposed.

"As it turns out, exposed mantle rocks alter in such a way as to
absorb a lot of carbon," he explained. One approach to
sequestering man-made greenhouse gases "that has received a good
bit of attention is the fracturing of exposed peridotite to
increase the surface area of these rocks so that they can absorb
more carbon."

The scientists detailed their findings online Nov. 14 in the
journal Nature Geoscience.